The present invention relates to a frequency band filter.
It is pointed out that a frequency band filter selects a given frequency band and can be used as a band pass filter or as a band stop filter, depending on whether it is mounted in series or in parallel with respect to the device supplying the signal to be processed. It is known to obtain frequency band filters by using a plurality of resonator cavities coupled to one another. Each cavity generally comprises a coaxial line terminated by a short circuit, determining a voltage node of the standing wave system established in the line. The different cavities of a frequency band filter, which are constructed separately, can be arranged in the vicinity of one another and coupled together, for example by plate capacitors. It is also known to obtain band filters by using cavities, whereof the outer conductor of the coaxial line serves as the inner conductor for the coaxial line of another cavity.
The prior art frequency band filters have numerous disadvantages and reference is made to certain of these below:
The large number of assemblies, by pressure or by welding, involved in the manufacture thereof, so that manufacturing costs are high.
Their complicated construction which, in the case of high power filters, makes it difficult for the air intended for cooling the conductors to circulate and consequently to prevent ionization of the air in certain regions.
The fact that the inter-cavity coupling means, which must be arranged as close as possible to the potential loops have to withstand generally high voltages, making their design difficult. These means also have series reactances, which are often prejudicial to performance characteristics.